for R1, R2 being Relation of F₁(),F₂() st ( for x being Element of F₁()
for y being Element of F₂() holds
( [x,y] in R1 iff P₁[x,y] ) ) & ( for x being Element of F₁()
for y being Element of F₂() holds
( [x,y] in R2 iff P₁[x,y] ) ) holds
R1 = R2