The forbidden built-in In the standard loopholes, the following is forbidden:


  Claiming that your answer is written in "MyOwnLanguage", where the command x means "read a sequence of numbers, split them into groups of three, and print the last numbers of those groups where the second number is less than the first"


Here, we are going to do the exact same thing.

Task

Given a sequence of positive integers, whose length is divisible by 3, split them into groups of three, and print the last numbers of those groups where the second number is less than the first.

Testcases

Input               Output
[]                  []
[1,2,3,4,5,6,7,8,9] []
[2,1,3,5,4,6,8,7,9] [3,6,9]
[3,1,4,1,5,9,2,6,5] [4]
[100,99,123]        [123]
[123,123,456]       []
[456,123,789]       [789]


Scoring

This is code-golf. Shortest answer in bytes wins.

Standard loopholes apply, so remember not to have a built-in command x that does this task.
Octave, 32 bytes

@(L)L(x=3:3:end)(diff(L)(x-2)&lt;0)

Try it online!
or
Verify test cases!
L3 = L(3:3:end)  %extract last elements of groups
d= diff(L)       % first difference of the list
y=d(1:3:end)     %extract first elements of each subgroup of the difference
idx = y&lt;0        %check for negative numbers  
result = L3(idx)