# Math ASCII Notation Demo

Mathematical content on Apronus.com is presented in Math ASCII Notation which can be properly displayed by all Web browsers because it uses only the basic set of characters found on all keyboards and in all fonts.

The purpose of these pages is to demonstrate the power of the Math ASCII Notation. In principle, it can be used to write mathematical content of any complexity. In practice, its limits can be seen when trying to write complicated formulas (containing, for example, variables with many indexes or multiple integrals).

Despite its limitations the Math ASCII Notation has much expressive power, as can be seen from browsing through these pages.

Let A,B,C,D,E,F be non-empty sets.
Suppose that (AxC) u (BxD) = ExF.
Suppose that A n B = O.
What can we conclude?
C = D
Take any d:-D. Choose some b:-B. Now (b,d):-BxD. Hence (b,d):- ExF.
Choose some (a,c):-AxC. Now (a,c):-ExF. We conclude that (a,d):- ExF.
Hence (a,d):-AxC or (a,d):-BxD. But a:-A and AnB=O, h
Let A,B,C,D be non-empty sets.
Prove that if A=B or C=D, then
(A x C) u (B x D) = (A u B) x (C u D).
___
Let J1 be a semi-ring in X, and J2 a semi-ring in Y.
Let u : J1 -> [0,oo] and y : J2 -> [0,oo] be additive.
Let J = { E x F : E:-J1 and F:-J2 }.
Let q : J -> |R*, q(E x F) = u(E) * y(F).
What can we conclude about q?
page 89 in 1st measure
Let W be a ring of sets.
Let y : W -> |R* be additive.
Prove that for every A,B :- W
y(A u B) + y(A n B) = ???
y(A u B) + y(A n B) = y(A) + y(B)
1) A u B = A u (B\A) disjointly
2) y(A u B) = y(A) + y(B\A)
3) y(A u B) + y(A n B) = y(A) + y(B\A) + y(B n A)
4) y(A u B) + y(A n B) = y(A) + y(B)
Let W be a ring of sets.
Let y : W -> |R* be additive.
Prove that for every A,B :- W
y(A) + y(B) = ???
y(A) + y(B) = y(A u B) + y(A n B)
PROOF:
0) A u B = A u (B\A) disjointly
1) y(A u B) + y(A n B) = y(A) + y(B\A) + y(B n A)
2) y(A u B) + y(A n B) = y(A) + y(B)
Let (T,>) be a directed set and let p:-T.
Let P = { t:-T : t > p }.
What can we say about (P,>) ?
(P,>) is also a directed set
Let W c P(X). Let A,B c X, x :- X.
Suppose that x is W-adherent to A u B.
What can we conclude?
page 53 in gen top
Let W c P(X), A,B c X.
Suppose that A,B are W-closed.
What can we conclude?
1) A u B is W-closed
2) A n B is W-closed
page 54 in gen top
Let W c P(X), A,B c X.
Suppose that A,B are W-open.
What can we conclude?
A n B is W-open, page 55 in gen top
A u B is W-open, page 56 in gen top
Let W c P(X). Let M c P(X) be a collection of W-closed sets.
What can we conclude?
//\\M is W-closed
page 55 in gen top