trim doesn't trim enough

[DanGrayson]

trafficstars

... as in this example:

i1 : R=QQ[x]

o1 = R

o1 : PolynomialRing

i2 : M=coker matrix {{1,x,0},{0,0,1}}

o2 = cokernel | 1 x 0 |
              | 0 0 1 |

                            2
o2 : R-module, quotient of R

i4 : M=coker matrix {{x,x^2,0},{0,0,1}}

o4 = cokernel | x x2 0 |
              | 0 0  1 |

                            2
o4 : R-module, quotient of R

i6 : N = trim M

o6 = subquotient (| 1 |, | 0 x |)
                  | 0 |  | 1 0 |

                               2
o6 : R-module, subquotient of R

i9 : P = subquotient ( map(R^2, R^1, {{1},{0}}), matrix {{x},{0}} )

o9 = subquotient (| 1 |, | x |)
                  | 0 |  | 0 |

                               2
o9 : R-module, subquotient of R

i11 : g = inducedMap ( N,P )

o11 = | 1 |

o11 : Matrix

i12 : isIsomorphism g

o12 = true

HT: @eisenbud