InstallGlobalFunction( homalgIOMode,
  function( arg )
    local nargs, mode, s;
    
    nargs := Length( arg );
    
    if nargs = 0 or ( IsString( arg[1] ) and arg[1] = "" ) then
        mode := "default";
    elif IsString( arg[1] ) then	## now we know, the string is not empty
        s := arg[1];
        if LowercaseString( s{[1]} ) = "a" then
            mode := "all";
        elif LowercaseString( s{[1]} ) = "b" then
            mode := "basic";
        elif LowercaseString( s{[1]} ) = "d" then
            mode := "debug";
        elif LowercaseString( s{[1]} ) = "f" then
            mode := "file";
        elif LowercaseString( s{[1]} ) = "p" then
            mode := "picto";
        else
            mode := "";
        fi;
    else
        Error( "the first argument must be a string\n" );
    fi;
    
    if mode = "default" then
        ## reset to the default values
        HOMALG_IO.color_display := false;
        HOMALG_IO.show_banners := true;
        HOMALG_IO.save_CAS_commands_to_file := false;
        HOMALG_IO.DoNotDeleteTemporaryFiles := false;
        HOMALG_IO.SaveHomalgMaximumBackStream := false;
        HOMALG_IO.InformAboutCASystemsWithoutActiveRings := true;
        SetInfoLevel( InfoHomalgToCAS, 1 );
        homalgMode( );
    elif mode = "all" then
        homalgIOMode( "debug" );
        homalgIOMode( "file" );
    elif mode = "basic" then
        HOMALG_IO.color_display := true;
        HOMALG_IO.show_banners := true;
        SetInfoLevel( InfoHomalgToCAS, 4 );
        homalgMode( "basic" );	## use homalgIOMode( "basic", "" ) to reset
    elif mode = "debug" then
        HOMALG_IO.color_display := true;
        HOMALG_IO.show_banners := true;
        SetInfoLevel( InfoHomalgToCAS, 8 );
        homalgMode( "debug" );	## use homalgIOMode( "debug", "" ) to reset
    elif mode = "file" then
        HOMALG_IO.save_CAS_commands_to_file := true;
    elif mode = "picto" then
        HOMALG_IO.color_display := true;
        HOMALG_IO.show_banners := true;
        SetInfoLevel( InfoHomalgToCAS, 4 );
        homalgMode( "logic" );	## use homalgIOMode( "picto", "" ) to reset
    fi;
    
    if nargs > 1 and IsString( arg[2] ) then
        CallFuncList( homalgMode, arg{[ 2 .. nargs ]} );
    fi;
    
end );

io_info_level := InfoLevel( InfoHomalgToCAS );

if not IsBound( pictogram ) then
    pictogram := HOMALG_IO.Pictograms.unknown;
    picto := pictogram;
elif io_info_level >= 3 then
    picto := pictogram;
    ## add colors to the pictograms
    if pictogram = HOMALG_IO.Pictograms.ReducedEchelonForm and
       IsBound( HOMALG_MATRICES.color_BOE ) then
        pictogram := Concatenation( HOMALG_MATRICES.color_BOE, pictogram, "\033[0m" );
    elif pictogram = HOMALG_IO.Pictograms.BasisOfModule and
      IsBound( HOMALG_MATRICES.color_BOB ) then
        pictogram := Concatenation( HOMALG_MATRICES.color_BOB, pictogram, "\033[0m" );
    elif pictogram = HOMALG_IO.Pictograms.DecideZero and
      IsBound( HOMALG_MATRICES.color_BOD ) then
        pictogram := Concatenation( HOMALG_MATRICES.color_BOD, pictogram, "\033[0m" );
    elif pictogram = HOMALG_IO.Pictograms.SyzygiesGenerators and
      IsBound( HOMALG_MATRICES.color_BOH ) then
        pictogram := Concatenation( HOMALG_MATRICES.color_BOH, pictogram, "\033[0m" );
    elif pictogram = HOMALG_IO.Pictograms.BasisCoeff and
      IsBound( HOMALG_MATRICES.color_BOC ) then
        pictogram := Concatenation( HOMALG_MATRICES.color_BOC, pictogram, "\033[0m" );
    elif pictogram = HOMALG_IO.Pictograms.DecideZeroEffectively and
      IsBound( HOMALG_MATRICES.color_BOP ) then
        pictogram := Concatenation( HOMALG_MATRICES.color_BOP, pictogram, "\033[0m" );
    elif need_output or need_display then
        pictogram := Concatenation( HOMALG_IO.Pictograms.color_need_output,
                             pictogram, "\033[0m" );
    else
        pictogram := Concatenation( HOMALG_IO.Pictograms.color_need_command,
                             pictogram, "\033[0m" );
    fi;
else
    picto := pictogram;
fi;

if io_info_level >= 3 then
    if ( io_info_level >= 7 and not need_display ) or io_info_level >= 8 then
        ## print the pictogram, the prompt of the external system,
        ## and the sent command
        Info( InfoHomalgToCAS, 7, pictogram, " ", stream.prompt,
              L{[ 1 .. Length( L ) - 1 ]} );
    elif io_info_level >= 4 then
        ## print the pictogram and the prompt of the external system
        Info( InfoHomalgToCAS, 4, pictogram, " ", stream.prompt, "..." );
    else
        ## print the pictogram only
        Info( InfoHomalgToCAS, 3, pictogram );
    fi;
    
fi;

Pictograms := rec(
  
  ##
  ## colors:
  ##
  
  ## pictogram color of a "need_command" or assignment operation:
  color_need_command                      := "\033[1;33;44m",
  
  ## pictogram color of a "need_output" or "need_display" operation:
  color_need_output                       := "\033[1;34;43m",
  
  ##
  ## good morning computer algebra system:
  ##
  
  ## initialize:
  initialize                              := "ini",
  
  ## define macros:
  define                                  := "def",
  
  ## get time:
  time                                    := ":ms",
  
  ## memory usage:
  memory                                  := "mem",
  
  ## unknown:
  unknown                                 := "???",
  
  ##
  ## external garbage collection:
  ##
  
  ## delete a variable:
  delete                                  := "xxx",
  
  ## delete serveral variables:
  multiple_delete                         := "XXX",
  
  ## trigger the garbage collector:
  garbage_collector                       := "grb",
  
  ##
  ## create lists:
  ##
  
  ## define a list:
  CreateList                              := "lst",
  
  ##
  ## create rings:
  ##
  
  ## define a ring:
  CreateHomalgRing                        := "R:=",
  
  ## get the names of the "variables" defining the ring:
  variables                               := "var",
  
  ## define zero:
  Zero                                    := "0:=",
  
  ## define one:
  One                                     := "1:=",
  
  ## define minus one:
  MinusOne                                := "-:=",
  
  ##
  ## mandatory ring operations:
  ##
  
  ## get the name of an element:
  ## (important if the CAS pretty-prints ring elements,
  ##  we need names that can be used as input!)
  ## (install a method instead of a homalgTable entry)
  homalgSetName                           := "\"a\"",
  
  ## a = 0 ?
  IsZero                                  := "a=0",
  
  ## a = 1 ?
  IsOne                                   := "a=1",
  
  ## substract two ring elements
  ## (needed by SimplerEquivalentMatrix in case
  ##  CopyRow/ColumnToIdentityMatrix are not defined):
  Minus                                   := "a-b",
  
  ## divide the element a by the unit u
  ## (needed by SimplerEquivalentMatrix in case
  ##  DivideEntryByUnit is not defined):
  DivideByUnit                            := "a/u",
  
  ## important ring operations:
  ## (important for performance since existing
  ##  fallback methods cause a lot of traffic):
  
  ## is u a unit?
  ## (mainly needed by the fallback methods for matrices, see below):
  IsUnit                                  := "?/u",
  
  ##
  ## optional ring operations:
  ##
  
  ## copy an element:
  CopyElement                             := "a>a",
  
  ## add two ring elements:
  Sum                                     := "a+b",
  
  ## multiply two ring elements:
  Product                                 := "a*b",
  
  ## the (greatest) common divisor:
  Gcd                                     := "gcd",
  
  ## cancel the (greatest) common divisor:
  CancelGcd                               := "ccd",
  
  ## random polynomial:
  RandomPol                               := "rpl",
  
  ## numerator:
  Numerator                               := "num",
  
  ## denominator:
  Denominator                             := "den",
  
  ## evaluate polynomial:
  Evaluate                                := "evl",
  
  ## degree of a multivariate polynomial
  DegreeOfRingElement                     := "deg",
  
  ## is irreducible:
  IsIrreducible                           := "irr",
  
  ##
  ## create matrices:
  ##
  
  ## define a matrix:
  HomalgMatrix                            := "A:=",
  
  ## copy a matrix:
  CopyMatrix                              := "A>A",
  
  ## load a matrix from file:
  LoadHomalgMatrixFromFile                := "A<<",
  
  ## save a matrix to file:
  SaveHomalgMatrixToFile                  := "A>>",
  
  ## get a matrix entry as a string:
  MatElm                  := "<ij",
  
  ## set a matrix entry from a string:
  SetMatElm                  := ">ij",
  
  ## add to a matrix entry from a string:
  AddToMatElm                := "+ij",
  
  ## get a list of the matrix entries as a string:
  GetListOfHomalgMatrixAsString           := "\"A\"",
  
  ## get a listlist of the matrix entries as a string:
  GetListListOfHomalgMatrixAsString       := "\"A\"",
  
  ## get a "sparse" list of the matrix entries as a string:
  GetSparseListOfHomalgMatrixAsString     := ".A.",
  
  ## assign a "sparse" list of matrix entries to a variable:
  sparse                                  := "spr",
  
  ## list of assumed inequalities:
  Inequalities                            := "<>0",
  
  ## list of assumed inequalities:
  MaximalIndependentSet                   := "idp",
  
  ##
  ## mandatory matrix operations:
  ##
  
  ## test if a matrix is the zero matrix:
  ## CAUTION: the external system must be able to check
  ##          if the matrix is zero modulo possible ring relations
  ##          only known to the external system!
  IsZeroMatrix                            := "A=0",
  
  ## number of rows:
  NrRows                                  := "#==",
  
  ## number of columns:
  NrColumns                               := "#||",
  
  ## determinant of a matrix over a (commutative) ring:
  Determinant                             := "det",
  
  ## create a zero matrix:
  ZeroMatrix                              := "(0)",
  
  ## create a initial zero matrix:
  InitialMatrix                           := "[0]",
  
  ## create an identity matrix:
  IdentityMatrix                          := "(1)",
  
  ## create an initial identity matrix:
  InitialIdentityMatrix                   := "[1]",
  
  ## "transpose" a matrix (with "the" involution of the ring):
  Involution                              := "A^*",
  
  ## get certain rows of a matrix:
  CertainRows                             := "===",
  
  ## get certain columns of a matrix:
  CertainColumns                          := "|||",
  
  ## stack to matrices vertically:
  UnionOfRows                             := "A_B",
  
  ## glue to matrices horizontally:
  UnionOfColumns                          := "A|B",
  
  ## create a block diagonal matrix:
  DiagMat                                 := "A\\B",
  
  ## the Kronecker (tensor) product of two matrices:
  KroneckerMat                            := "AoB",
  
  ## multiply a ring element with a matrix:
  MulMat                                  := "a*A",
  
  ## multiply a matrix with a ring element:
  MulMatRight                             := "A*a",
  
  ## add two matrices:
  AddMat                                  := "A+B",
  
  ## substract two matrices:
  SubMat                                  := "A-B",
  
  ## multiply two matrices:
  Compose                                 := "A*B",
  
  ## pullback a matrix by a ring map:
  Pullback                                := "pbk",
  
  ##
  ## important matrix operations:
  ## (important for performance since existing
  ##  fallback methods cause a lot of traffic):
  ##
  
  ## test if two matrices are equal:
  ## CAUTION: the external system must be able to check
  ##          equality of the two matrices modulo possible ring relations
  ##          only known to the external system!
  AreEqualMatrices                        := "A=B",
  
  ## test if a matrix is the identity matrix:
  IsIdentityMatrix                        := "A=1",
  
  ## test if a matrix is diagonal (needed by the display method):
  IsDiagonalMatrix                        := "A=\\",
  
  ## get the positions of the zero rows:
  ZeroRows                                := "0==",
  
  ## get the positions of the zero columns:
  ZeroColumns                             := "0||",
  
  ## get "column-independent" unit positions
  ## (needed by ReducedBasisOfModule):
  GetColumnIndependentUnitPositions       := "ciu",
  
  ## get "row-independent" unit positions
  ## (needed by ReducedBasisOfModule):
  GetRowIndependentUnitPositions          := "riu",
  
  ## get the position of the "first" unit in the matrix
  ## (needed by SimplerEquivalentMatrix):
  GetUnitPosition                         := "gup",
  
  ## position of the first non-zero entry per row
  PositionOfFirstNonZeroEntryPerRow       := "fnr",
  
  ## position of the first non-zero entry per column
  PositionOfFirstNonZeroEntryPerColumn    := "fnc",
  
  ## indicator matrix of non-zero entries
  IndicatorMatrixOfNonZeroEntries         := "<>0",
  
  ## transposed matrix:
  TransposedMatrix                        := "^tr",
  
  ## divide an entry of a matrix by a unit
  ## (needed by SimplerEquivalentMatrix in case
  ##  DivideRow/ColumnByUnit are not defined):
  DivideEntryByUnit                       := "ij/",
  
  ## divide a row by a unit
  ## (needed by SimplerEquivalentMatrix):
  DivideRowByUnit                         := "-/u",
  
  ## divide a column by a unit
  ## (needed by SimplerEquivalentMatrix):
  DivideColumnByUnit                      := "|/u",
  
  ## divide a row by a unit
  ## (needed by SimplerEquivalentMatrix):
  CopyRowToIdentityMatrix                 := "->-",
  
  ## divide a column by a unit
  ## (needed by SimplerEquivalentMatrix):
  CopyColumnToIdentityMatrix              := "|>|",
  
  ## set a column (except a certain row) to zero
  ## (needed by SimplerEquivalentMatrix):
  SetColumnToZero                         := "|=0",
  
  ## get the positions of the rows with a single one
  ## (needed by SimplerEquivalentMatrix):
  GetCleanRowsPositions                   := "crp",
  
  ## convert a single row matrix into a matrix
  ## with specified number of rows/columns
  ## (needed by the display methods for homomorphisms):
  ConvertRowToMatrix                      := "-%A",
  
  ## convert a single column matrix into a matrix
  ## with specified number of rows/columns
  ## (needed by the display methods for homomorphisms):
  ConvertColumnToMatrix                   := "|%A",
  
  ## convert a matrix into a single row matrix:
  ConvertMatrixToRow                      := "A%-",
  
  ## convert a matrix into a single column matrix:
  ConvertMatrixToColumn                   := "A%|",
  
  ##
  ## basic matrix operations:
  ##
  
  ## compute a (r)educed (e)chelon (f)orm:
  ReducedEchelonForm                      := "ref",
  
  ## compute a "(bas)is" of a given set of module elements:
  BasisOfModule                           := "bas",
  
  ## compute a reduced "(Bas)is" of a given set of module elements:
  ReducedBasisOfModule                    := "Bas",
  
  ## (d)e(c)ide the ideal/submodule membership problem,
  ## i.e. if an element is (0) modulo the ideal/submodule:
  DecideZero                              := "dc0",
  
  ## compute a generating set of (syz)ygies:
  SyzygiesGenerators                      := "syz",
  
  ## compute a generating set of reduced (Syz)ygies:
  ReducedSyzygiesGenerators               := "Syz",
  
  ## compute a (R)educed (E)chelon (F)orm
  ## together with the matrix of coefficients:
  ReducedEchelonFormC                     := "REF",
  
  ## compute a "(BAS)is" of a given set of module elements
  ## together with the matrix of coefficients:
  BasisCoeff                              := "BAS",
  
  ## (D)e(C)ide the ideal/submodule membership problem,
  ## i.e. write an element effectively as (0) modulo the ideal/submodule:
  DecideZeroEffectively                   := "DC0",
  
  ##
  ## optional matrix operations:
  ##
  
  ## Hilbert-Poincare series of a module:
  HilbertPoincareSeries                   := "HPs",
  
  ## Hilbert polynomial of a module:
  HilbertPolynomial                       := "Hil",
  
  ## affine dimension of a module:
  AffineDimension                         := "dim",
  
  ## affine degree of a module:
  AffineDegree                            := "adg",
  
  ## the constant term of the hilbert polynomial:
  ConstantTermOfHilbertPolynomial         := "P_0",
  
  ## primary decomposition:
  PrimaryDecomposition                    := "YxZ",
  
  ## eliminate variables:
  Eliminate                               := "eli",
  
  ## leading module:
  LeadingModule                           := "led",
  
  ## the i-th monomial matrix
  MonomialMatrix                          := "mon",
  
  ## matrix of symbols:
  MatrixOfSymbols                         := "smb",
  
  ## leading module:
  ## coefficients:
  Coefficients                            := "cfs",
  
  ##
  ## optional module operations:
  ##
  
  ## compute a better equivalent matrix
  ## (field -> row+col Gauss, PIR -> Smith, Dedekind domain -> Krull, etc ...):
  BestBasis                               := "(\\)",
  
  ## compute elementary divisors:
  ElementaryDivisors                      := "div",
  
  ##
  ## for the eye:
  ##
  
  ## display objects:
  Display                                 := "dsp",
  
  ## the LaTeX code of the mathematical entity:
  homalgLaTeX                             := "TeX",
  
)