is an attribute that can be assigned to a symbol f to indicate that all expressions involving nested functions f should be flattened out. This property is accounted for in pattern matching.
- Flat corresponds to the mathematical property of associativity.
- For a symbol f with attribute Flat, f[f[a,b],f[c]] is automatically reduced to f[a,b,c].
- Functions like Plus, Times, and Dot are Flat.
- For a Flat function f, the variables x and y in the pattern f[x_,y_] can correspond to any sequence of arguments.
- The Flat attribute must be assigned before defining any values for a Flat function.
Introduced in 1988