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Block

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Block[{x, y, ...}, expr]

temporarily removes the definitions of the given variables, evaluates expr, and restores the original definitions afterwards.

Block[{x=$x_0$, y=$y_0$, ...}, expr]

assigns temporary values to the variables during the evaluation of expr.

• • n = 10

• • Block[{n = 5}, n ^ 2]

• • n

Values assigned to block variables are evaluated at the beginning of the block.
Keep in mind that the result of Block is evaluated again, so a returned block variable
will get its original value.

• • Block[{x = n+2, n}, {x, n}]

If the variable specification is not of the described form, an error message is raised.

• • Block[{x + y}, x]

Variable names may not appear more than once:

• • Block[{x, x}, x]