The command evalindets is a particular combination of calls to eval and indets that allows you to efficiently transform all subexpressions of a given type by some algorithm. It encapsulates a common "pattern" used in expression manipulation and transformation.

Each subexpression of type atype is transformed by the supplied transformer procedure to produce a "replacement" for it. Then, each subexpression is replaced in the original expression using eval with the corresponding transformed expression.

The flat option indicates that the subexpressions of expr of type atype are not nested. This provides a hint to Maple that it can use a somewhat faster algorithm in this special case. If the flat option is passed and nesting occurs, unexpected results may be be produced.