Evaluate an expression with x locally set to 7:

Locally set both x and y:

With works even without evaluation:

Define the local variable y in terms of the earlier local variable x:

Use With to insert values into held expressions:

Use := to insert the unevaluated form of an expression into the result:

Compare with the following:

The variable names can be the same:

Use a constant for a value that is needed more than once:

Set multiple variables with independent values:

Set multiple variables with later values depending on earlier values:

With allows inserting values into unevaluated expressions:

Local variables declared within a single list are independent of each other:

Local variables declared in subsequent lists depend on the variables declared in earlier lists:

With[def₁,def₂,expr] is equivalent to With[def₁,With[def₂,expr]]:

Using x:=x₀ inserts the unevaluated form of x₀, which then evaluates based on its surroundings:

Using x=x₀ evaluates x₀ once and inserts the result everywhere x appears:

Module introduces local variables to which values can be assigned:

With variables are read only:

With is faster than Module:

Block localizes values only; it does not substitute values. Module creates new symbols:

With allows substitution inside an unevaluated expression, preserving nested scopes:

Ordinary substitution does not preserve scoping:

With is a scoping construct; variables are renamed in nested scopes:

Build the function from its elements to avoid the renaming:

The notebook interface by default warns if a variable is declared at multiple levels:

This valid syntax uses the last value in the function body, as would be the case with literal nesting:

Find a zero of an arbitrary function using Newton's method:

Find a fixed point:

A version of With where the initializer is within the scope of the local variable:

Here the f inside the function definition is not inside its own scope: