• x is any valid variable, a function name, or a matrix of names. x cannot be a number or an expression.

• b is any expression that can be evaluated. If b contains other variables, then those variables must also be defined globally above the definition of x.

• You cannot override a global definition using a local definition.

• You cannot have more than one global definition of the same variable in a worksheet or in a parent worksheet that includes other worksheets.

• You cannot use the global definition operator inside a solve block.