normal takes as argument an expression.
The expression is considered as a rational fraction with respect
to generalized identifiers
(either true identifiers or transcendental functions replaced by
a temporary identifiers) with coefficients in ℚ or ℚ[i]
or in an algebraic extension (e.g. ℚ[√2]).
normal returns the expanded irreducible representation
of this rational fraction. See also ratnormal for pure rational
fractions or simplify if the transcendental functions are
not algebraically independant.