deffunc H₁( set , set , set ) -> set = G . $1,$3;
ex M being ManySortedSet of [:I,I,I:] st
for i, j, k being set st i in I & j in I & k in I holds
M . i,j,k = H₁(i,j,k) from ALTCAT_1:sch 3();
hence ex b₁ being ManySortedSet of [:I,I,I:] st
for i, j, k being set st i in I & j in I & k in I holds
b₁ . i,j,k = G . i,k ; :: thesis: verum