A very distinctive feature of Metafont is the use of equations to define variables. A numeric variable (or component of a pair or transformation variable) may be in the three states "known" (set), "unknown independent" (not set), and "unknown dependent" (not set, but given by a linear expression of one or several independents). When Metafont executes an equation statement, it turns one of the independents involved into a dependent and eliminates it from the expressions for all other dependents; when no independents remain in the expression for a dependent variable, that variable becomes known. Solving "linear" equation systems thus is a built-in feature of the Metafont language, and the recommended method of assigning most variables (especially those whose values have geometric significance) is to state equations determining their values. Equation systems frequently mix numeric (scalar) equations with pair (vector) equations.