Completely logical and solvable without assuming symmetry.
@VitaMaskar if you want to try: On the first line you can think what would happen, if you put the 7 at the c1-7 and what it implies on line 2. If so, then line 2 will have c1-3 and c5, while you can't put anything on c4 and c6-7 (X). This means, that the second 3 on line 2 can not be set in this setting(as long as line 1 c4 is filled). Hence line 1 c1-4 are not fillable (X). You can repeat the same at the end and you'll have the first line filled :)
If you have difficulties imagining it, you can start and try with temporaries - with enough training you won't have to use them anymore.
@VitaMaskar if you want to try:
On the first line you can think what would happen, if you put the 7 at the c1-7 and what it implies on line 2.
If so, then line 2 will have c1-3 and c5, while you can't put anything on c4 and c6-7 (X). This means, that the second 3 on line 2 can not be set in this setting(as long as line 1 c4 is filled).
Hence line 1 c1-4 are not fillable (X).
You can repeat the same at the end and you'll have the first line filled :)
If you have difficulties imagining it, you can start and try with temporaries - with enough training you won't have to use them anymore.
Thanks.