Description
This html file is part of the project "Principia Mathematica II" see project homepage. Here we introduce the formal language and the deduction rules. This is done in an informal way, important theorems (e.g.: universal decomposition, and any proofs) are left out.
All we will do is manipulating symbols. We build symbol strings and use certain simple rules to get new symbol strings. So by starting with a few basic strings we create a whole universe of derived symbol strings. It turns out that these strings could be interpreted as a view to the incredible world of mathematics.
See derived theorems of propositional calculus and derived theorems of predicate calculus
The following symbols are used:
' Ù ',
' Ú ',
' Þ ',
' Û ',
' Ø ',
' $ ',
' " ',
'x', 'y', 'z', 'u', 'v', 'w', 'r', 's', 't', 'a', 'b', 'c', 'd',
'P', 'Q', 'A', 'B', 'C', 'D',
'R', 'F', 'G', 'H', 'I', 'J',
'0' , '1', '2', '3', '4', '5', '6', '7', '8', '9',
'(' , ')', ','
.
We call any of the following strings atomic formula:
Now we define recursively formulas and the relations free and bound for these strings:
Now we build strings made of these symbols. Strings are finite sequences of symbols, the length of a string is the length of the sequence. In this article whitespace of strings is ignored.
We call
number all (nonempty) strings that are entirely made of
'0' , '1', '2', '3', '4', '5', '6', '7', '8', '9'
but don't start with '0'.
With quantifier we denote the strings
"$"
and
"""
.
We call proposition variables
all strings that look like
"P", "Q", "A", "B", "C", "D" or "P" + number.
All strings of the form "x", "y", "z", "u", "v", "w", "r", "s", "t", "a", "b", "c", "d" or "x" + number are called subject variables.
With predicate variable we denote strings that look like
"R", "F", "G", "H", "I", "J" or "R" + number.
Ù"
+ q + ")"
Let p be a string that is a formula and let q be a substring of p. q is called a part formula of q if it is a formula (and the next symbol is no digit).
The following strings are examples for formulas. (White space is ignored.)
Ù (Q Ù P))"
Ù Q Ù P)"
After the basic language definitions we could now take a look at the deduction rules. Deduction rules enable us to deduct new formulas from a basic set of formulas called axioms. We also have a list of abbreviations for certain operators. To prove a proposition we use rules to get a sequence of formulas: the proof lines. We use a deduction rule on our axioms, abbreviations, already proved sentences and proof lines to achive a new proof line. The proof is finished if the last proof line is identical to the proposition.
add axiom
parameters:
label | reference name for an axiom |
add sentence
parameters:
label | reference name for a proposition |
modus ponens
parameters:
n | proof line number |
m | proof line number |
replace proposition variable
parameters:
A | proposition variable |
p | formula |
n | proof line number |
replace predicate variable
parameters:
A | atomic formula with predicate variable |
p | formula |
n | proof line number |
rename bound subject variable
parameters:
X | subject variable |
Y | subject variable |
n | proof line number |
m | occurence number |
rename free subject variable
parameters:
X | subject variable |
Y | subject variable |
n | proof line number |
generalize a formula
parameters:
n | proof line number |
m | occurence number |
particularization
parameters:
X | subject variable |
n | proof line number |
use abbreviation
parameters:
label | reference name for an abbreviation |
n | proof line number |
m | occurence number |
reverse abbreviation
parameters:
label | reference name for an abbreviation |
n | proof line number |
m | occurence number |