2. Upper-case letters' A' through' z' may exist; if so, they are alphabetically ordered, but not necessarily consecutive (e.g., 'A' < 'B'). 

3. Lower-case letters' a' through' z' may exist; if so, they are alphabetically ordered, but not necessarily consecutive (e.g., ' a' < ' b'). 

The predeclared functions ord and chr allow the mapping of the character set onto the ordinal numbers of the character set - and vice versa; ord and chr are called transfer functions. 

ord(C) is the ordinal number of the character C in the underlying ordered character set. 

chr (I) is the character value with the ordinal number I. 

i.e., You can see immediately that ord and chr are inverse functions, 

chr(ord(C)) = C and ord (chr (1)) = I 

Furthermore, the ordering of a given character set is defined by 

C1 < C2 iff ord(C1) < ord(C2) 

This definition can be extended to each of the relational operators: <>, <, <=, >=, >. If R denotes one of these operators, then 

C1 R C2 iff ord(C1) R ord(C2) 

When the argument ofthe predeclared functions pred and succ is of type Char, the functions can be defined as: 

pred (C) succ(C) chr (ord (C) -1) chr(ord(C)+l) 

Note: The predecessor (successor) of a character is dependent upon the underlying character set. The two properties hold only if the predecessor or successor exists. 

## 2.E. The Type Real 

A value of type Real is an element of the implementation-defined subset of real numbers. 

