Dup
From WikiManual
Operators:
Duplicate Stack Operator UNARY
Places an additional copy of the top value in the stack on the stack. Thus:
5 dup
will place two 5s on top of the stack.
Duplicate Stack Operator UNARY
Places an additional copy of the top value in the stack on the stack. Thus:
5 dup
will place two 5s on top of the stack.