- § 86. Nature of the variable
- § 87. Relation of the variable to
*any* - § 88. Formal and restricted variables
- § 89. Formal implication presupposes
*any* - § 90. Duality of
*any*and*some* - § 91. The class-concept
*propositional function*is indefinable - § 92. Other classes can be defined by means of
*such that* - § 93. Analysis of the variable

§ 87 n. 1. Here there is a

where `c`,`c` is any class, is defined as equivalent to If

↩`p` implies `p`, and

implies `x` is a `c``p` for all values of `x`, then `p` is true.

§ 87 n. 2. Was sind und was sollen die Zahlen? Brunswick, 1893. ↩

§ 87 n. 3. Allgemeine Arithmetik, Leipzig, 1885. ↩

The Principles of Mathematics was written by Bertrand Russell, and published in in 1903. It is now available in the Public Domain.