Underlying Types

[gs]

I was looking through the MISRA 2 Standard and was wondering what the underlying type of an expression is involving mixed types. For example suppose we are given the following variables:
int i1, i2, *ip;
unsigned char uc;
float f;
What is the underlying type of:
i1 | uc;
i2 ? i1 : uc;
&i1;
ip;
( i1 == i2 );
f;
Since the Standard goes into such detail regarding the concept of \"underlying type\", I feel this is an important issue which, to me, requires clarification.