gap> nul2:= NullspaceMat(TransposedMat(rev));
[ [ 1, 0, 0, 1, 0, 0, -a, b, 0, ab^2, 0, 0, 0, 2ab^2, ab^2, -2a^2b^2, 0, 0, 
      ab^3, 0, 0, ab^4, ab^4, 0, 0, 0, 0, 0, 0, 0, -ab^6, 0, 0, ab^8, 0, 0, 
      b^8, ab^8, 0, -a^2b^8+b^9, b^10, 0, ab^9, b^10, b^10, 0, 0, 0 ], 
  [ 0, 1, 0, 0, 0, 1, 1, -2a, 0, b^2, 0, 0, 0, b^2, b^2, -ab^2, 0, 0, 0, 0, 
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
      0, 0, 0, 0 ], 
  [ 0, 0, 1, -a, 0, 0, 0, -ab, ab^2, -a^2b^2, b^2, 0, 0, -a^2b^2, -a^2b^2, 
      -ab^3+a^3b^2, 0, b^5, b^4, 0, 0, b^5, b^5, 0, 0, 0, b^6, -ab^6, 0, 0, 
      0, -ab^7, ab^8, -a^2b^8, b^8, 0, 0, -a^2b^8, -a^2b^8, -ab^9+a^3b^8, 0, 
      b^11, b^10, 0, 0, b^11, b^11, 0 ], 
  [ 0, 0, 0, 0, 1, -a, -a, a^2, b^2, -ab^2, 0, b^2, 0, -ab^2, -ab^2, a^2b^2, 
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, b^6, -ab^6, -ab^6, a^2b^6, b^8, 
      -ab^8, 0, b^8, 0, -ab^8, -ab^8, a^2b^8, 0, 0, 0, 0, 0, 0, 0, 0 ], 
  [ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, -a, -a, b+a^2, b^2, 0, 0, b^2, 
      b^2, -ab^2, -ab^2, 0, b^4, 0, 0, b^4, 0, 0, 0, b^5, 0, 0, 0, 0, 0, 0, 
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ], 
  [ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ]
    , [ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
      0, 0, 1, 0, 0, 0, 1, 1, -2a, 0, b^2, 0, 0, 0, b^2, b^2, -ab^2, 0, 0, 0, 
      0, 0, 0, 0, 0 ], 
  [ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1 
     ] ]
gap> nul1:= NullspaceMat(TransposedMat(dif));
[ [ 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ]
    , [ 0, 1, 1, 0, 0, b^-1, 1, 0, 0, -b^-2, -b^-2, 0, 0, b^-3, -b^-2, ab^-3, 
      0, -b^-4+a^2b^-5, -b^-4+a^2b^-5, 0, -2ab^-5+2a^3b^-6, b^-5, 
      -b^-4+a^2b^-5, -ab^-5+2a^3b^-6, 0, b^-6+a^2b^-7-2a^4b^-8, 
      b^-6+a^2b^-7-2a^4b^-8, -ab^-7+2a^3b^-8, -ab^-7+2a^3b^-8, b^-7, b^-6, 
      -ab^-7+2a^3b^-8, 0, -2b^-8+2a^2b^-9, -2b^-8+2a^2b^-9, -ab^-9+2a^3b^-10, 
      0, b^-9, -2b^-8+a^2b^-9+2a^4b^-10, ab^-9, 3ab^-10-4a^3b^-11-4a^5b^-12, 
      -2b^-10+2a^2b^-11+2a^4b^-12, -2b^-10+2a^2b^-11+2a^4b^-12, 0, -ab^-11, 
      b^-11, -2b^-10+2a^2b^-11+2a^4b^-12, 0 ], 
  [ 0, 0, 0, 1, 1, ab^-1, 0, 1, 0, a^-1b^-1-ab^-2, a^-1b^-1, b^-2, 0, 0, 
      a^-1b^-1, 0, 0, a^-1b^-3-2ab^-4, a^-1b^-3-ab^-4, 0, 2b^-4-2a^2b^-5, 0, 
      a^-1b^-3-ab^-4, 2b^-4-2a^2b^-5, 0, -ab^-6+2a^3b^-7, -ab^-6+2a^3b^-7, 
      2b^-6-2a^2b^-7, 2b^-6-2a^2b^-7, ab^-7, 0, 2b^-6-2a^2b^-7, 0, 
      2a^-1b^-7-3ab^-8, 2a^-1b^-7-2ab^-8, 2b^-8-2a^2b^-9, 0, 0, 
      2a^-1b^-7-ab^-8-2a^3b^-9, 0, -3b^-9+4a^2b^-10+4a^4b^-11, 
      2a^-1b^-9-3ab^-10-2a^3b^-11, 2a^-1b^-9-2ab^-10-2a^3b^-11, 0, b^-10, 0, 
      2a^-1b^-9-2ab^-10-2a^3b^-11, b^-10 ], 
  [ 0, 0, 0, 0, 0, 0, 0, 0, 1, -a^-1, -a^-1, 0, 0, 0, -a^-1, 0, 0, -a^-1b^-2, 
      -a^-1b^-2, 0, -2b^-3, 0, -a^-1b^-2, -2b^-3, 0, 2ab^-5, 2ab^-5, -2b^-5, 
      -2b^-5, 0, 0, -2b^-5, 0, -2a^-1b^-6, -2a^-1b^-6, -2b^-7, 0, 0, 
      -2a^-1b^-6-2ab^-7, 0, 4b^-8+4a^2b^-9, -2a^-1b^-8-2ab^-9, 
      -2a^-1b^-8-2ab^-9, 0, 0, 0, -2a^-1b^-8-2ab^-9, 0 ], 
  [ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, b^-2, a^2b^-3, 
      0, ab^-2, a^2b^-3, 0, -a^3b^-5, -a^3b^-5, a^2b^-5, a^2b^-5, 0, 0, 
      a^2b^-5, 0, ab^-6, ab^-6, a^2b^-7, b^-6, 0, ab^-6+a^3b^-7, b^-6, 
      -3a^2b^-8-2a^4b^-9, ab^-8+a^3b^-9, ab^-8+a^3b^-9, b^-8, 0, 0, 
      2ab^-8+a^3b^-9, 0 ], 
  [ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, b^-1, 0, 0, 
      b^-1, 0, -ab^-3, -ab^-3, b^-3, b^-3, 0, 0, b^-3, 0, a^-1b^-4, a^-1b^-4, 
      b^-5, 0, 0, a^-1b^-4+ab^-5, 0, -2b^-6-2a^2b^-7, a^-1b^-6+ab^-7, 
      a^-1b^-6+ab^-7, 0, 0, 0, a^-1b^-6+ab^-7, 0 ], 
  [ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
      1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ]
    , [ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
      0, 0, 0, 0, 0, 0, 0, 0, 0, 1, -a^-1, -a^-1, 0, 0, 0, -a^-1, 0, 2b^-2, 
      -a^-1b^-2, -a^-1b^-2, 0, 0, 0, -a^-1b^-2, 0 ] ]
gap> LogTo();