Epimers of glucose

When sugars are different from one another, only in configuration with regard to a single carbon atom, other than the reference carbon atom, they are called epimers. For example, glucose and mannose are an epimeric pair which differs only with respect to C2. Similarly, galactose is the 4th epimer of glucose. (Fig. 6.4). Galactose and mannose are not epimers but diastereoisomers.Ref: DM Vasudevan, 7th edition, page no: 77