<<< mml $$\genfrac{}{}{.2ex}{}{\frac{a}{b}}{\frac{c}{d}}=\genfrac{}{}{.2ex}{}{\frac{a}{b}}{\frac{c}{d}}$$ >>> native [ EFraction NormalFrac (EFraction NormalFrac (EIdentifier "a") (EIdentifier "b")) (EFraction NormalFrac (EIdentifier "c") (EIdentifier "d")) , ESymbol Rel "=" , EFraction NormalFrac (EFraction NormalFrac (EIdentifier "a") (EIdentifier "b")) (EFraction NormalFrac (EIdentifier "c") (EIdentifier "d")) ]