source(ComplexMap) -- get the source of a map of chain complexes

i1 : R = ZZ/101[a..d]

o1 = R

o1 : PolynomialRing

i2 : I = ideal(a^2, b^2, c^2)

             2   2   2
o2 = ideal (a , b , c )

o2 : Ideal of R

i3 : J = I + ideal(a*b*c)

             2   2   2
o3 = ideal (a , b , c , a*b*c)

o3 : Ideal of R

i4 : FI = freeResolution I

      1      3      3      1
o4 = R  <-- R  <-- R  <-- R
                           
     0      1      2      3

o4 : Complex

i5 : FJ = freeResolution J

      1      4      6      3
o5 = R  <-- R  <-- R  <-- R
                           
     0      1      2      3

o5 : Complex

i6 : f = randomComplexMap(FJ, FI, Cycle=>true)

          1              1
o6 = 0 : R  <---------- R  : 0
               | 24 |

          4                        3
     1 : R  <-------------------- R  : 1
               {2} | 24 0  0  |
               {2} | 0  24 0  |
               {2} | 0  0  24 |
               {3} | 0  0  0  |

          6                        3
     2 : R  <-------------------- R  : 2
               {4} | 24 0  0  |
               {4} | 0  0  0  |
               {4} | 0  0  0  |
               {4} | 0  24 0  |
               {4} | 0  0  0  |
               {4} | 0  0  24 |

          3                    1
     3 : R  <---------------- R  : 3
               {5} | 24c  |
               {5} | -24b |
               {5} | 24a  |

o6 : ComplexMap

i7 : source f

      1      3      3      1
o7 = R  <-- R  <-- R  <-- R
                           
     0      1      2      3

o7 : Complex

i8 : assert isWellDefined f

i9 : assert isComplexMorphism f

i10 : assert(source f == FI)

i11 : assert(target f == FJ)

i12 : kk = coker vars R

o12 = cokernel | a b c d |

                             1
o12 : R-module, quotient of R

i13 : F = freeResolution kk

       1      4      6      4      1
o13 = R  <-- R  <-- R  <-- R  <-- R
                                   
      0      1      2      3      4

o13 : Complex

i14 : source dd^F == F

o14 = true

i15 : target dd^F == F

o15 = true

i16 : degree dd^F == -1

o16 = true