SymPy Gamma

Input:

rsolve(y(n+2)-y(n+1)-y(n), y(n), {y(0): 0, y(1): 1})

Error:

rsolve(y(n+2)-y(n+1)-y(n), y(n), {y(0): 0, y(1): 1})

unsupported operand type(s) for *: 'UndefinedFunction' and 'Add'

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