A to Z relearnt

A- Applied mathematics/Alpha
B-Bessel Functions
C-Continuous in space and Time/Caley Hamilton Theorem
D-Discrete/Delta Function
E- Eigen Function Expansion
F-Fourier Transform
G-Gauss Divergence theorem
H-Henkel Functions
I-Imaginary
J-Jacobians
K-Kronaker Delta
L-Lorentz attraction/Lagrange Mutipliers/Laplace Transforms
M-Multi connected domains
N-Newtonian differentiations
O-ODE
P-PDE
Q-Quasilinear
R-Runge-Kutta/Roots Test
S-Singularity/Similarity Solutions
T-Taylor Series Expansion
U-Undetermined Coefficients method to solve ODEs
V-Variation of Parameters method to solve ODEs
W-Wave Equation
X-
Y-YYZ-?
Z-Z-transform

ps: help me with x and y.