Write three anonymous functions in R and assign them to variables as described below:

• Create an anonymous function that adds 3 to its input and assign it to the variable add_three.
• Create an anonymous function that returns TRUE if a number is even, and assign it to the variable is_even.
• Create an anonymous function that concatenates two strings (with no separator), and assign it to the variable concat_strings.

Each function should be assigned to the specified variable name. Do not use named function definitions for this task.