sign "⊦" from Frege's 1879 Begriffsschrift: "(I)t may be read 'it is true that'" Thus to assert a proposition p PM writes: "⊦. p." (PM 1927:92) (Observe that, as in the original, the left dot is square and of greater size than the period on the right.) Most of the rest of the notation in PM was invented by Whitehead. An introduction to the notation of "Section A Mathematical Logic" (formulas ✸1–✸5.71) PMs dots are used in a manner similar to parentheses. Each dot (or multiple dot) represents either a left or right parenthesis or the logical symbol ∧. More than one dot indicates the "depth" of the parentheses, for example, ".", ":" or ":.", "::". However the position of the matching right or left parenthesis is not indicated explicitly in the notation but has to be deduced from some rules that are complex and at times ambiguous. Moreover, when the dots stand for a logical symbol ∧ its left and right operands have to be deduced using similar rules. First one has to decide based on context whether the dots stand for a left or right parenthesis or a logical symbol. Then one has to decide how far the other corresponding parenthesis is: here one carries on until one meets either a larger number of dots, or the same number of dots next that have equal or greater "force", or the end of the line. Dots next to the signs ⊃, ≡,∨, =Df have greater force than dots next to (x), (∃x) and so on, which have greater force than dots indicating a logical product ∧. Example 1. The line ✸3.4. ⊢ : p . q . ⊃ . p ⊃ q corresponds to ⊢ ((p ∧ q) ⊃ (p ⊃ q)). The two dots standing together immediately following the assertion-sign indicate that what is asserted is the entire line: since there are two of them, their scope is greater than that of any of the single dots to their right. They are replaced by a left parenthesis standing where the dots are and a right parenthesis at the end of the formula, thus: ⊢ (p . q . ⊃ . p ⊃ q). (In practice, these outermost parentheses, which enclose an entire formula, are usually suppressed.) The first of the single dots, standing between two propositional variables, represents conjunction. It belongs to the third group and has the