The meaning of symbols " £ ", " ³ ", " i " and " Û "? I am learning Linear Algebra right now and I am seeing some new symbols. These are from my schools online document. I can write the exact examples they're used at:
In the natural number set we can also define the ³ relation:

n ³ m (we say that m is greater or equal than n) when m < n or m = n.

Theorem:

The relation ³ has the following properties:

    n ³ n,
    (m £ n and m ³ n ) Þ (m = n),
    (m ³ n and n ³ k) Þ (m ³ k),
    For every pair n, m either m £ n or m ³ n,
    n ³ 0.

And for the i and Û symbol,
Definition

Complex numbers are ordered pairs of two real numbers e.g. (a, b), (c, d), with equality, addition and multiplication defined as follows:
( a, b ) = ( c, d ) Û a = c i b = d

So for the "³" symbol, I understand the meaning but because that I couldn't find any document that uses this in any website, I got curious if it's a right symbol or not. And for the others, I just couldn't really get them.
Thanks!
 A: You are a victim of mojibake.
The characters you're seeing are from the Windows-1252 character encoding, in which:

*

*£ = 0xA3

*³ = 0xB3

*Û = 0xDB

*Þ = 0xDE

But it appears that the author's intention was to render the characters in the Symbol font, in which:

*

*0xA3 = ≤

*0xB3 = ≥

*0xDB = ⇔

*0xDE = ⇒
So, just search and replace these character codes, to get:
In the natural number set we can also define the ≥ relation:

n ≥ m (we say that m is greater or equal than n) when m < n or m = n.

Theorem:

The relation ≥ has the following properties:

    n ≥ n,
    (m ≤ n and m ≥ n ) ⇒ (m = n),
    (m ≥ n and n ≥ k) ⇒ (m ≥ k),
    For every pair n, m either m ≤ n or m ≥ n,
    n ≥ 0.

Definition

Complex numbers are ordered pairs of two real numbers e.g. (a, b), (c, d), with equality, addition and multiplication defined as follows:
( a, b ) = ( c, d ) ⇔ a = c ∧ b = d

The odd character out is i, which is encoded as 0x69, corresponding to Symbol character ι (Greek small letter iota).  This doesn't make sense in context, but Symbol character 0xD9 = ∧ (Logical AND) does.  Somehow, a few bits got mangled in transit.  I've manually made this correction above.
