## A Birthday −A−B−C(E−F) by KevGar

### Puzzle explanation

The initials of extra words in clues spelt “squares”, hinting that the letters A to F represent the first six square numbers: 1, 4, 9, 16, 25 and 36 respectively. Thematic entries are the nicknames of symphonies by Joseph Haydn, clued by their numbers. The title is A Birthday Surprise, referencing the “Surprise” Symphony, No. 94. Haydn was born on 31 March 1732.

For the “Hen” Symphony, No. 83, the expected expression was A−B+C+D+E+F. Extra brackets, eg A−(B−C)+D+E+F, were accepted as long as they didn't change the value of the expression.

### Clue explanations

Conventions: * = anagram, < = reversal

Across
1   (SCHOOLMASTER) Symphony 55 = 1 + 4 + 9 + 16 + 25
10   PROPOLIS PRO + POLISH − H
12 shoddy HALO (c)H(e)A(p) L(o)O(k)
13   SARSEN EN(s) after SARS
15   INKLE KINDLE * − (downloa)D
16   (CLOCK) Symphony 101 = 1 + 4 × 25
17   LASS LASSIE − IE
18 queen’s CACOLET COLE in CAT
19   OVOIDAL VOID in OA(k) + L
23   TABOR OR after BAT <
24   SAINS SANS around I
26   (MERCURY) Symphony 43 = -9 + 16 + 36
27   COCKPIT COCK + TIP <
29   BAMS AB < + MS
32 urethane PATIO (s)P(r)A(y) T(h)I(s) O(n)
33   DEPOT DEP(art) + TO <
34   ASLOPE A + POLES *
35 author ECCO E(ighth) + C + C + O
36   (DRUMROLL) Symphony 103 = 4 − 9 × (25 − 36)
37   RECREATIONAL REC + RATIONAL around E(P)
Down
2   CRENA ANE < after CR
3   HONKS (HOST − T) around NK
4 resting OOSE (l)OOSE(n)
5   LLAMA (A + MALL) <
6   (MIRACLE) Symphony 96 = -4 + 9 × 16 × 25 / 36
7   SHELLAC HELL in SAC(k)
8   ELECTOR E + LECTOR
9 engraving ROCK CRYSTAL (ROCKERY − E) around C + LAST *
10   (PHILOSOPHER) Symphony 22 = 1 − 4 + 25
11   PALS SLAP <
14   SCOT SCOUT − U
20   VACANCE VACAN(t) + CE
21   INCISOR (ROSSINI − S(onata) + C) *
22   AMPHORA CAMPHOR − C + A
25 Scottish SKOL SOL around K(ing)
28   INPUT (I + NUT) around P
29   (BEAR) Symphony 82 = 1 − 9 × (16 − 25)
30   APRON (PAN + OR) *
31   MOLLA MOLL + A
33   DEMI- (lea)D(ing) (plan)E(tary) (move)M(ent’s) (ecl)I(pse)