Merges a list of pyQuil programs into a single one by appending them in sequence.
    If multiple programs in the list contain the same gate and/or noisy gate definition
    with identical name, this definition will only be applied once. If different definitions
    with the same name appear multiple times in the program list, each will be applied once
    in the order of last occurrence.

    :param list prog_list: A list of pyquil programs
    :return: a single pyQuil program
    :rtype: Program

def merge_programs(prog_list):
    """
    Merges a list of pyQuil programs into a single one by appending them in sequence.
    If multiple programs in the list contain the same gate and/or noisy gate definition
    with identical name, this definition will only be applied once. If different definitions
    with the same name appear multiple times in the program list, each will be applied once
    in the order of last occurrence.

    :param list prog_list: A list of pyquil programs
    :return: a single pyQuil program
    :rtype: Program
    """
    definitions = [gate for prog in prog_list for gate in Program(prog).defined_gates]
    seen = {}
    # Collect definitions in reverse order and reapply definitions in reverse
    # collected order to ensure that the last occurrence of a definition is applied last.
    for definition in reversed(definitions):
        name = definition.name
        if name in seen.keys():
            # Do not add truly identical definitions with the same name
            # If two different definitions share a name, we include each definition so as to provide
            # a waring to the user when the contradictory defgate is called.
            if definition not in seen[name]:
                seen[name].append(definition)
        else:
            seen[name] = [definition]
    new_definitions = [gate for key in seen.keys() for gate in reversed(seen[key])]

    p = sum([Program(prog).instructions for prog in prog_list], Program())  # Combine programs without gate definitions

    for definition in new_definitions:
        p.defgate(definition.name, definition.matrix, definition.parameters)

    return p