Chapter II of Shalosh B. Ekhad's

"66 Skyscrapers Problems"

Thirty (Medium) 4 by 4 Problems

[Note: This kind of puzzle is due to Wei-Hwa Huang and appears every Sunday (2016) in the New York Times Magazine]

Problem 1
Problem 2
Problem 3
Problem 4
Problem 5
Problem 6
Problem 7
Problem 8
Problem 9
Problem 10
Problem 11
Problem 12
Problem 13
Problem 14
Problem 15
Problem 16
Problem 17
Problem 18
Problem 19
Problem 20
Problem 21
Problem 22
Problem 23
Problem 24
Problem 25
Problem 26
Problem 27
Problem 28
Problem 29
Problem 30