Avery , Blake , Clark and Doyle each live in an apartment. Their apartment are arranged like this :

          +---+---+---+---+
          | A | B | C | D |  --> East
          +---+---+---+---+

1. One of the four is the landlord.
2. If Clark's apartment is not next to Blake's apartment, then the landlord is Avery & lives in apartment A.
3. If Avery's apartment is east of Clark's apartment, then the landlord is Doyle and lives in apartment D.
4. If Blake's apartment is not next to Doyle's apartment, then the landlord is Clark and lives in apartment C.
5. If Doyle's apartment is east of Avery's apartment, then the landlord is Blake and lives in apartment B.

Who is the landlord?

To begin with, I liked this puzzle and appreciated lowering the level of difficulty.
I will address this issue later after explaining my process of thought.
In Boolean algebra the statement " if XXX then YYY" means : either XXX is false or YYY is true or both.

Take two statements like: 
Stat.I  :   if all Eskimos live in Africa then 7>5,
Stat.iI  :  if all Eskimos live in Africa then 7<5.   Both statements are true and convey the followinmessage:  IF the XXX part is false - no need to read the rest.  
Now back to our apartments. Let us denote by adbc an arrangement in which the
tenant a lives in the 1^st
from the West apt, d in the 2^nd etc, no landlord specified, while dbaC means THAT the tenant d lives in the 1^st from the West apt, b in the 2^nd etc, and the landlord is C. 

Reading the 2^nd part of the
2-5  statements one grasps immediately that the "results" are mutually exclusive, so there are only 4 IGs (initial guesses)":Axxx,  xBxx, xxCx, xxxD   (x denotes a regular tenant, not the owner).

Starting with any initial guess, checking it against the conditional statement  and modifying it when needed, amd/or backtracking upon contradiction you arrive to the right solution in no time.
I   have started with abcd, statements 2 and 3  were in the "no need to read the rest" category; statement 4 implied
a change either to adCb or daCb
and statement 5 left only one valid answer I.e. daCb.

My interpretation of "One of them was a landlord", was and is "Only one of them was a landlord".  

Assuming also that ONLY ONE POSSIBLE  solution exists, I stopped here.
Done.  D1.  

One might argue that I was lucky with my choice of IG,
-just for fun I've tried two other IGs and in both cases it was a very short process reaching the same conclusion. 

Maybe D1 is not a must and D2 SEEMS A REASONABLE COMPROMISE, but in no way a logical  puzzle solvable like  this one justifies a  D3.

To end with a ppositive note: GOOD PUZZLE!  

Edited on February 8, 2013, 1:23 pm

Posted by Ady TZIDON on 2013-02-08 13:14:15