Piecewise[{{val1, cond1}, {val2, cond2}, ...}] represents a piecewise function with values vali in the regions defined by the conditions condi. Piecewise[{{val1, cond1}, ...}, val] uses default value val if none of the condi apply. The default for val is 0.

Constant is an attribute that indicates zero derivative of a symbol with respect to all parameters.

| short notations Piecewise | piecewise