| ⊦ valid-group-nodes(prefixn(n, gndx + mkgnode(nd, m, boolvar, false) ')) = valid-group-nodes(prefixn(n, gndx)) |
⊦ prefixn(n, gndx) = (n ≤ # gndx ⊃ firstn(n, gndx);gndx)
⊦ valid-group-nodes ((n ≤ #(gndx + mkgnode(nd, m, boolvar, false) ') ⊃ firstn(n, gndx + mkgnode(nd, m, boolvar, false) ');gndx + mkgnode(nd, m, boolvar, false) ')) = valid-group-nodes(prefixn(n, gndx))
Used terms: gndx + mkgnode(nd, m, boolvar, false) ', n