Critical point exponents inequalities - The Coopersmith inequolity

[LagrangeEuler]

The Coopersmith inequolity:
T=T_c, H\rightarrow 0^+

I'm confused by few things. What means H\rightarrow 0^+? And what difference will be if H\rightarrow 0^-? And what means T=T_c if we can't measure T_c in experiments?

Then there is relation M \sim H^{\frac{1}{\delta}}
That means if I understand well that
\frac{1}{\delta}=\lim_{H\rightarrow 0}\frac{lnM(H)}{lnH}
Correct?

 

[LagrangeEuler]

Any answer?