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IsInvertible

check if a RINGELEM is invertible

Syntax 
IsInvertible(f: RINGELEM): BOOL

Description
This function tests whether the argument f is invertible in RingOf(f) .

Example 
/**/  use R ::= QQ[x];
/**/  Q := R/ideal(x^2+1);
/**/  use Q;
/**/  IsInvertible(x-2);
true
/**/ 1/(x-2);
((-1/5)*x -2/5)