isExactRes -- Test whether a chain complex is exact.

i1 : R = QQ[x_1..x_4,z_1..z_4]

o1 = R

o1 : PolynomialRing

i2 : I =  ideal(z_2*z_3-z_1*z_4,x_4*z_3-x_3*z_4,x_2*z_2-x_1*z_4,x_4*z_1-x_3*z_2,x_2*z_1-x_1*z_3)

o2 = ideal (z z  - z z , x z  - x z , x z  - x z , x z  - x z , x z  - x z )
             2 3    1 4   4 3    3 4   2 2    1 4   4 1    3 2   2 1    1 3

o2 : Ideal of R

i3 : cc= res I

      1      5      5      1
o3 = R  <-- R  <-- R  <-- R  <-- 0
                                  
     0      1      2      3      4

o3 : ChainComplex

i4 : isExactRes cc

o4 = true