\displaylines - to display any number of centered formulas (without any alignment).
{ \displaylines{ <math> \cr <repeat as needed> } }
\displaylines command is used to display any number of centered formulas. a double-backslash can be used in place of the \cr; the final \\ or \cr is optional.
\displaylines{ a = a\\ \text{if } a=b \text{ then } b=a\\ \text{if } a=b \text{ and } b=c \text{ then } a=c }