Operators

Operator	Function
NOT	complement
AND	logical and
OR	logical or
NAND	logical complement of and
NOR	logical complement of or
XOR	logical exclusive or
XNOR	logical complement of exclusive or
=	test for equality
/=	test for inequality
<	test for less than
<=	test for less than or equal
>	test for greater than
>=	test for greater than or equal

Example

If ((a AND b) = '1')
{
    ...
}

Use a different clock for Process

rising_edge([clk name]) falling_edge([clk name])

If (Reset = '0') 
{
    ...
}
Elsif (rising_edge(clk_50)) 
{
    ...
}