$($a$)$Use the SML system to define a datatype for labeled three branch trees, the trees with

possible zero, one, two, or three branches. Using integers to label the nodes of the trees. No

polymorphic definition for this problem. Your definition needs to be accepted by SML$.$

$($b$)$ Draw a concrete three branch tree of at least $20$ nodes but no more than $35$ nodes. There must

be some one, two, and three branches in your tree. The integers labeling the nodes range from

$40$ to $75$ and each node has only one integer label. Represent this concrete three branch tree

by using your three branch tree datatype definition. Your representation needs to be accepted

by SML as an instance of the datatype you defined in $($a$).$

$($c$)$ Use fun in SML to define a function that performs on any three branch tree of the datatype

you defined in $($a$).$ This function sums all integer labels in the tree. Your definition needs to

be accepted by SML$.$

$($d$)$ Apply this function to your concrete three branch tree, as represented using the datatype you

defined, to check the correctness of the result