/**
 * Check if a date is valid
 * @param date - date to validate
 */
export declare function isValidDate(date: Date | string | number): boolean;
/**
 * Check if a year is a leap year
 * @param year - year to check
 */
export declare function isLeapYear(year: number): boolean;
/**
 * Check if a date is in the past
 * @param date - date to check
 */
export declare function isPast(date: Date): boolean;
/**
 * Check if a date is in the future
 * @param date - date to check
 */
export declare function isFuture(date: Date): boolean;
/**
 * Check if a date is today
 * @param date - date to check
 */
export declare function isToday(date: Date): boolean;
/**
 * Check if a date is yesterday
 * @param date - date to check
 */
export declare function isYesterday(date: Date): boolean;
/**
 * Check if a date is tomorrow
 * @param date - date to check
 */
export declare function isTomorrow(date: Date): boolean;
/**
 * Check if two dates are the same day
 * @param date1 - first date
 * @param date2 - second date
 */
export declare function isSameDay(date1: Date, date2: Date): boolean;
/**
 * Check if a date is a weekend (Saturday or Sunday)
 * @param date - date to check
 */
export declare function isWeekend(date: Date): boolean;
/**
 * Check if a date is a weekday (Monday through Friday)
 * @param date - date to check
 */
export declare function isWeekday(date: Date): boolean;
/**
 * Check if a time string is valid (HH:MM or HH:MM:SS format)
 * @param time - time string to validate
 */
export declare function isValidTimeString(time: string): boolean;
/**
 * Check if a date string is valid ISO 8601 format
 * @param dateString - date string to validate
 */
export declare function isValidISOString(dateString: string): boolean;
/**
 * Check if two dates are in the same week (ISO week, Monday-Sunday)
 * @param date1 - first date
 * @param date2 - second date
 */
export declare function isSameWeek(date1: Date, date2: Date): boolean;
/**
 * Check if two dates are in the same month
 * @param date1 - first date
 * @param date2 - second date
 */
export declare function isSameMonth(date1: Date, date2: Date): boolean;
/**
 * Check if two dates are in the same year
 * @param date1 - first date
 * @param date2 - second date
 */
export declare function isSameYear(date1: Date, date2: Date): boolean;
/**
 * Check if a date is in the current week
 * @param date - date to check
 */
export declare function isThisWeek(date: Date): boolean;
/**
 * Check if a date is in the current month
 * @param date - date to check
 */
export declare function isThisMonth(date: Date): boolean;
/**
 * Check if a date is in the current year
 * @param date - date to check
 */
export declare function isThisYear(date: Date): boolean;
/**
 * Check if a date is a business day (weekday, optionally excluding holidays)
 * @param date - date to check
 * @param holidays - optional array of holiday dates to exclude
 */
export declare function isBusinessDay(date: Date, holidays?: Date[]): boolean;
/**
 * Check if a date is in the last N days (including today)
 * @param date - date to check
 * @param n - number of days
 */
export declare function isInLastNDays(date: Date, n: number): boolean;
/**
 * Check if a date is in the next N days (including today)
 * @param date - date to check
 * @param n - number of days
 */
export declare function isInNextNDays(date: Date, n: number): boolean;
/**
 * Check if two dates are in the same hour
 * @param date1 - first date
 * @param date2 - second date
 */
export declare function isSameHour(date1: Date, date2: Date): boolean;
/**
 * Check if two dates are in the same minute
 * @param date1 - first date
 * @param date2 - second date
 */
export declare function isSameMinute(date1: Date, date2: Date): boolean;
/**
 * Check if two dates are in the same second
 * @param date1 - first date
 * @param date2 - second date
 */
export declare function isSameSecond(date1: Date, date2: Date): boolean;
/**
 * Check if a date is in a specific quarter
 * @param date - date to check
 * @param quarter - quarter (1-4)
 */
export declare function isInQuarter(date: Date, quarter: 1 | 2 | 3 | 4): boolean;
/**
 * Check if two dates are in the same quarter
 * @param date1 - first date
 * @param date2 - second date
 */
export declare function isSameQuarter(date1: Date, date2: Date): boolean;
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