Consider the relation {{MATH_1}}. Which of the following are valid expressions for {{MATH_2}}? {{CMD_3}} {{CMD_4}}{{MATH_5}}{{CMD_6}} {{CMD_7}}{{MATH_8}}{{CMD_9}} {{CMD_10}}{{MATH_11}}{{CMD_12}} {{CMD_13}}{{MATH_14}}{{CMD_15}} {{CMD_16}} {{CMD_17}} {{CMD_18}}